Chemical mechanical polishing (CMP) has been widely adopted in semiconductor manufacturing process for planarization of a layer, especially a copper layer, on a wafer surface. More specifically, a copper layer is deposited over a dielectric layer to fill openings within the dielectric layer. To remove portions of the copper layer that are not within the openings (i.e., to form interconnects that are electrically isolated from each other), a slurry and a pad are used. Typically, the wafer is rinsed immediately following planarization (i.e., while the wafer is still in contact with the pad) to remove any unwanted surface defects, such as slurry particles or other residuals. Additional rinsing may be performed after transferring the wafer to a scrubber or noncontact cleaning tool to remove any surface defects that were not removed during the rinse on the pad.
Due to the complex nature of the chemistry and CMP process, it is possible that components of the slurry react with the copper layer to form defects on the surface of the wafer because as the amount of copper that is exposed during planarization increases (e.g. an increase in the number of openings and/or the size of openings), the number of surface defects also increases. The surface defects are typically less than 1 centimeter in area and are commonly referred to as stains, precipitates, carbon particles, carbon residual, slurry residual, or organic residuals. Much is unknown as to the exact cause and the exact composition of the surface precipitates. However, they are believed to be clusters, of material that include carbon. It is desirable to decrease the number of surface defects as they lead to yield loss.
One proposed solution to minimize defects is to use polyethylene glycol (PEG) as a surfactant in the slurry. However, the addition of PEG does not consistently decrease surface defects. In addition, concentrations in excess of 1 weight percent (10000 ppm) of PEG may need to be added to the slurry. The relatively high concentration of PEG can cause several problems including poor filtration and has a negative cost impact. Therefore, there is a need for a reliable solution to minimize surface defects that does not require large additive concentrations.
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